spi: cadence_qspi: Do not return unset error code

In spi_calibration if the low range fails to calibrate then the code
attempted to return the variable err but this has not been set in this
case. Instead just return -EIO.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>

drivers/spi/cadence_qspi.c

@@ -142,7 +142,7 @@ static int spi_calibration(struct udevice *bus, uint hz)
 
 	if (range_lo == -1) {
 		puts("SF: Calibration failed (low range)\n");
-		return err;
+		return -EIO;
 	}
 
 	/* Disable QSPI for subsequent initialization */